Internal combustion engines

Abstract

A two stroke internal combustion engine (5) having a transfer port (9) and an exhaust port (8) in a cylinder (6) which are opened and closed in a timed relationship by the reciprocating movement of a piston (7). The exhaust port (8) communicates with an exhaust passage that is tuned to provide a pressure pattern in the exhaust passage that will create at the exhaust port (8) a predetermined pressure pattern while the exhaust port (8) is open. Coolant is supplied to the exhaust passage when the engine is subject to increasing transient load conditions, at engine speeds below the tuned speed, and at a controlled rate to establish a tuned state in the exhaust passage during the transient condition.

I claim: 
     
       1. A method of operating an internal combustion engine having a cylinder with a piston movable therein defining a combustion chamber, a charge inlet port and an exhaust port in said cylinder, said ports being arranged to be opened and closed in a timed relation to the movement of the piston in the cylinder so the inlet port is open during at least part of the time the exhaust port is open and closes before the exhaust port is closed, the method including the steps of: delivering the gaseous products of combustion from the cylinder to an exhaust passage communicating with the exhaust port downstream thereof, said exhaust passage being dimensionally proportioned to establish when the engine is operating in a first selected speed range a pressure pattern in the gas in the exhaust passage in response to opening of the exhaust port that will create at the exhaust port a pressure pulse of predetermined character before the exhaust port closes, and, in response to a predetermined engine operating condition existing when the engine is operating in a second speed range outside of said first selected speed range and having a lower limit of 1.6 times the normal idle speed of the engine, regulating the temperature of the gas in the exhaust passage in relation to the engine speed and load to establish a pressure pattern in said exhaust passage in response to opening of the exhaust port to create a pressure pulse of said predetermined character at the exhaust port before the exhaust port closes when the engine is operating in said second speed range outside of said first selected speed range. 
     
     
       2. A method of operating an internal combustion engine as claimed in claim 1 wherein the exhaust gas temperature is regulated to create said character of pressure pulse in response to predetermined engine load conditions on the engine when operating in said second speed range. 
     
     
       3. A method of operating an internal combustion engine as claimed in claim 1 wherein the exhaust gas temperature is regulated to create said character of pressure pulse at all loads within the second speed range. 
     
     
       4. A method of operating an internal combustion engine as claimed in claim 1, wherein the exhaust gas temperature is regulated to create said character of pressure pulse in response to a predetermined rate of increase of load on the engine when operating in said second speed range. 
     
     
       5. A method of operating an internal combustion engine as claimed in any one of claims 1 to 4, wherein the lower limit of said second speed range is in the range of 1300 RPM to 1800 RPM. 
     
     
       6. A method of operating an internal combustion engine as claimed in claim 4, wherein coolant is admitted to the exhaust passage to regulate the temperature of the exhaust gas therein, said coolant being admitted at a rate related to the engine speed, said admission of coolant being initiated in response to the existence of a predetermined rate of increase in engine load and is maintained for a selected time period. 
     
     
       7. A method of operating an internal combustion engine as claimed in claim 6, wherein the admission of coolant is maintained for a time period proportional to the initial rate of change of the engine load. 
     
     
       8. A method of operating an internal combustion engine as claimed in claim 4, 6 or 7, wherein said second speed range is from 1.2 times the normal engine idle speed to the lower limit of said first selected speed range. 
     
     
       9. A method of operating an internal combustion engine as claimed in any one of claims 1 to 4, wherein the exhaust passage is dimensionally proportioned so said pressure pulse is at a pressure below the pressure existing in the combustion chamber at the time the pressure pulse arrives at the exhaust port, and arrives at the exhaust port before the inlet port has closed. 
     
     
       10. A method of operating an internal combustion engine as claimed in claim 9 wherein said pressure of the predetermined pressure pulse is below atmospheric pressure. 
     
     
       11. A method of operating an internal combustion engine as claimed in any one of claims 1 to 4, wherein the exhaust passage is dimensionally proportioned so the pressure pulse is at a pressure above the pressure existing in the combustion chamber and arrives at the exhaust port after the inlet port closes and before the exhaust port closes. 
     
     
       12. An internal combustion engine having a cylinder with a piston movable therein defining a combustion chamber, a charge inlet port and an exhaust port in said cylinder, said ports being arranged to be opened and closed in a timed relation to the movement of the piston in the cylinder so the inlet port is open during at least part of the time the exhaust port is open and is closed before the exhaust port is closed, and an exhaust passage communicating with the exhaust port downstream thereof, said exhaust passage being dimensionally proportioned to establish when the engine is operating in a first selected speed range a pressure pattern in the gas in the exhaust passage in response to opening of the exhaust port that will create at the exhaust port a pressure pulse of predetermined character before the exhaust port closes, means operable when the engine is operating in a second speed range outside of said first selected speed range and having a lower limit of 1.6 times the normal idle speed of the engine to regulate the temperature of the gas in the exhaust passage in relation to the engine speed and load to establish a pressure pattern in said exhaust passage in response to opening of the exhaust port to create a pressure pulse of said predetermined character at the exhaust port before the exhaust port closes, and activator means responsive to a predetermined engine operating condition to activate said means to regulate the exhaust gas temperature when the engine is operating in said second speed range outside of said first selected speed range. 
     
     
       13. An internal combustion engine as claimed in claim 12 wherein said activator means is responsive to a predetermined engine load condition. 
     
     
       14. An internal combustion engine as claimed in claim 12 wherein said activator means is a responsive to all load conditions within said second speed range. 
     
     
       15. An internal combustion engine as claimed in claim 12 wherein said activator means is responsive to a predetermined rate of increase of load on the engine when operating in second speed range. 
     
     
       16. An internal combustion engine as claimed in claim 15, wherein said regulator means is adapted to admit coolant to said exhaust passage at a rate proportional to the engine speed, and said activator means is adapted to initiate the admission of coolant in response to a predetermined rate of increase in engine load and to maintain said admission of coolant for a selected time period. 
     
     
       17. An internal combustion engine as claimed in claim 15 or 16, wherein said activator means is adapted to maintain said admission of coolant for a time period proportional to the initial rate of change of engine load. 
     
     
       18. An internal combustion engine as claimed in claim 16, wherein said regulator means comprises a valve control port communicating with the exhaust passage to admit coolant thereto when said port is open, and means to control the degree of opening of said port proportional to the engine speed. 
     
     
       19. An internal combustion engine as claimed in claim 15, including pump means driven by the engine to provide coolant to the regulator means at a pressure proportional to engine speed, for admission to the exhaust passage, and the activator means includes a valve means controlling the supply of coolant from the pump means to the regulator means, said valve means being adapted to open to permit the supply of coolant to the regulator means in response to a rate of increase of pressure of the coolant from the pump means above a predetermined value. 
     
     
       20. An internal combustion engine as claimed in claim 19, wherein said regulator means comprises a valve control port communicating with the exhaust passage to admit coolant thereto when said port is open, and means to control the degree of opening of said port proportional to the engine speed. 
     
     
       21. An internal combustion engine as claimed in claim 19 or 20, wherein the valve means includes a valve element normally closing a port through which coolant is supplied from the pump to the regulator means for delivery to the exhaust passage, actuator means to displace said valve element to open said port in response to a rate of increase of coolant pressure above said predetermined value, and means to return the valve element at a controlled rate to a position to close said port.